A printed circuit board in which a conductor circuit is formed on the surface of an insulating substrate has been widely used for electronic components and semiconductor devices. In recent years, an increase in density and a decrease in size of conductor circuits has been desired for printed circuit boards along with a demand for a decrease in size and an improvement in functions of electronic instruments.
In order to deal with this demand, a semi-additive method has been proposed as a method of producing a high-density printed circuit board. The semi-additive method includes subjecting the surface of an insulating substrate made of a synthetic resin to electroless copper plating, and etch-removing a copper foil layer formed by electroless plating to form a circuit pattern. It is possible to accurately form a minute circuit pattern by the semi-additive method.
However, the semi-additive method has the following drawbacks. Specifically, the copper foil layer formed between the insulating substrate and the circuit pattern by electroless plating substantially does not exhibit adhesion to the insulating substrate. Therefore, although adhesion between the circuit pattern and the insulating substrate is maintained due to the anchor effect of the copper foil layer when the surface of the insulating substrate has a relatively large roughness, adhesion between the circuit pattern and the insulating substrate is insufficient when the insulating substrate has a flat surface. In this case, the conductor circuit exhibits insufficient adhesion to the substrate.
A method which roughens the surface of the insulating substrate to increase adhesion of the conductor circuit has been proposed (Patent Document 1, etc.). Specifically, this method forms minute elevations and depressions on the surface of the insulating substrate.
However, when forming a more minute circuit pattern using this method, a high-density, super-fine circuit lines are affected by elevations and depressions formed on the surface of the insulating substrate. This may make it difficult to form a high-density conductor circuit.
In recent years, since a decrease in size and an increase in density of a circuit formed on a printed circuit board have been desired, a circuit-forming technique which does not decrease adhesion even when using an insulating substrate having a flat surface has been strongly desired.
A polyorganosiloxane compound having a ladder structure has been known as a polymer which forms a thin film which exhibits excellent hardness, heat resistance, weather resistance, and the like (Patent Documents 2 to 5, etc.). Patent Document 6 discloses that a resin composition containing a polyorganosiloxane compound having a hydroxyl group, an acrylic copolymer resin having an alcoholic hydroxyl group, and a polyisocyanate compound exhibits excellent adhesion to a metal (particularly aluminum).
However, Patent Documents 2 to 6 do not disclose that a polyorganosiloxane compound having a ladder structure serves as an adhesive which firmly bonds a metal or a synthetic resin.    Patent Document 1: JP-A-2003-49079    Patent Document 2: JP-A-58-59222    Patent Document 3: JP-A-7-70321    Patent Document 4: JP-A-8-92374    Patent Document 5: JP-A-6-306173    Patent Document 6: JP-A-10-87834